This invention relates to episcopic image projection systems, i.e., projection systems which reflect light from a graphic sheet onto a screen or other suitable surface. Such systems are distinguished from diascopic image projection systems wherein light passes through the graphic sheet en route to the screen. Because light in the episcopic system does not have to pass through the graphic sheet, opaque graphic sheets rather than transparent graphic sheets can be utilized. For this reason episcopic image projection systems are commonly referred to as opaque projectors.
Opaque projectors have the inherent advantage that plain paper graphics, and even three-dimensional objects, can be projected without special preparation. This, of course, eliminates the time and expense needed to prepare transparencies of each graphic which are required in diascopic image projection systems. Moreover, the use of plain paper graphics in opaque projectors gives the user an element of spontaneity and versatility during a visual presentation which is not available in diascopic systems.
In spite of their many benefits, opaque projectors have had limited commercial acceptance and success. Numerous factors such as coat, size, weight, operation difficulties, image diffusion and the like may account for this situation. Accordingly, there have been several attempts over the years to produce a compact, opaque projector which is capable of achieving excellent optical results. Some of these attempts are described in U.S. Pat. Nos. 3,947,103; 3,951,535; 3,915,5667; 3,837,739; 3,778,142; and Re. 28,274. Other image projection systems are disclosed in U.S. Pat. Nos. 3,900,253; 3,752,574; 3,257,898; 3,366,005; and 3,190,174. Nonetheless, the marketplace remains in need of an improved high quality, portable opaque projector.
Accordingly, it is a primary object of this invention to provide an improved opaque projector. Another object of this invention is the provision of such a projector which is sufficiently compact and portable as to enable it to be readily stored and transported yet sufficiently uncomplicated as to be easy to assemble and use. Other objects, features and advantages of the invention will become apparent hereinafter.